A conventional, publicly known arc start ancillary apparatus for an arc welding machine has been disclosed in Japanese Patent Application Laid-Open No. 8-215843.
As shown in FIG. 6, a conventional arc welding machine is made up of an arc start ancillary apparatus 19, a welding power source 10, a wire 6, a wire feeding motor 7, a base metal 8, and an electrode 9.
This arc welding machine is configured so that welding current is supplied to between the electrode 9 and the base metal 8 by means of the low-voltage welding power source 10 on receipt of a welding start signal, and thereby the wire feeding motor 7 is driven feed the wire 6 to a weld location, by which arc welding is performed.
At the time of arc start, spark discharge is generated between the base metal 8 and the electrode 9 by applying a pulsed D.C. high voltage, so that an insulating substance (for example, slug) at the tip end of the wire is destroyed by an electric shock of the generated spark discharge, or an arc is induced by the creeping discharge on the insulating substance on the base metal 8.
Thereby, the arc start performance is improved, and the safety is secured by restricting the effective value of current caused to flow at the time of discharge by the application of the pulse-form D.C. high voltage.
The conventional arc start ancillary apparatus 19 is made up of a D.C. high-voltage power source 1 for generating spark discharge, a capacitive load 2 for checking whether discharge is generated between the electrode 9 and the base metal 8, a timer circuit 3 for turning on/off the D.C. high-voltage power source 1 with a fixed period, a switch 4, and a drooping resistor 5.
The following operation is repeated: A D.C. high voltage is applied by the D.C. high-voltage power source 1 according to the input of a welding start signal, the current of spark discharge at the time when spark discharge is generated is detected by the capacitive load 2, the switch 4 of the D.C. high-voltage power source 1 is turned off according to the timer circuit 3, and the switch 4 of the D.C. high-voltage power source 1 is turned on again after an elapse of certain time.
Pulsing the D.C. high voltage of the D.C. high-voltage power source 1 is an effective way to decrease the effective value of current flow by discharging.
However, there arises a problem in that the current in transferring from spark discharge sometimes to arc discharge cannot sometimes be secured, so that arc is not started.
Also, although the aforesaid current can sometimes be secured by the floating capacitance by a cable or the like, the aforesaid current cannot be secured depending on the laying condition of cable.
Also, although the capacitive load 2 is provided in the conventional arc start ancillary apparatus 19, this capacitive load 2 serves to detect discharge, but is not intended to improve the arc start performance.